The Air Journal is OxiClear's magazine on air, breathing and the craft of masks. Issue two.
Some mornings the air looks fine and reads 320. Some evenings it looks apocalyptic and reads 140. Your eyes are a poor air sensor. The Air Quality Index is how you stop guessing.
What AQI actually measures
AQI is a translation layer. Monitoring stations measure individual pollutants: fine particles called PM2.5, coarser dust called PM10, and gases like ozone and nitrogen dioxide. The index converts the worst of them at that hour into one number on a 0 to 500 scale, so you can act without a chemistry degree.
That is the key to reading it: AQI reports the worst offender, not an average. On most north Indian city days, the number you see is being driven by particulate matter. That matters for what a mask can and cannot do, and we will get to it.
Why the number swings through the day
The air is not one thing all day. Overnight, cool calm air traps the previous evening's emissions near the ground, so early mornings often read worse than they look. Traffic stacks a second peak onto the evening. And from late October to January across north India, cooler air, calmer winds and seasonal smoke hold everything lower for longer. That is the smog season, and it is why the same commute can cost you double in November what it costs in August.
The practical habit: check the number at the hours you are actually outside. A reading at breakfast tells you about breakfast.
When to mask up
There is no magic threshold, and we will not invent one. But a practical pattern serves most people well. From the Poor band, around 201 and up, a mask starts earning its place on commutes, school runs and outdoor stretches. In Very Poor and Severe air, it earns its place the moment you step outside. People who feel pollution sooner, and anyone spending long hours on the road, tend to reach for it a band earlier.
What the mask is doing at those numbers: a reusable N99 mask with a clean filter and a close fit helps reduce exposure to airborne particles such as PM2.5, PM10, road dust and smoke particles. That covers the pollutants driving the number on most bad days. It is not a gas-protection product, and no mask replaces the better move of keeping the worst hours brief.
Fit decides whether any of this reaches your lungs. The one-minute routine is in our fit guide, and the ratings themselves are decoded in issue one.
Check your air before you head out
Our homepage runs a live Air Check: your location's current air, in the same band colours as the ladder above. Thirty seconds before you leave is the cheapest protection there is.
Take this with you
- AQI reports the worst pollutant right now, not an average. Higher is worse; the bands matter more than the digits.
- Check at the hours you are outside. Mornings and evenings usually read worst.
- From Poor, around 201 and up, a mask starts earning its place. From Very Poor, it earns it at the door.
- October to January is the season to watch in north India. Build the habit before the ladder climbs.
Browse the OxiClear N99 range, and keep a clean filter in rotation. The number changes daily; the routine should not.
Source: India's National Air Quality Index bands, Central Pollution Control Board (airquality.cpcb.gov.in).
